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CVE-2026-80585— mptcp: fastopen: only mark MPTFO subflows with SYN data

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

以下是该 Linux 内核漏洞描述的中文翻译： 在 Linux 内核中，已解决以下漏洞： MPTCP：FastOpen：仅对携带 SYN 数据的 MPTFO 子流进行标记 被动 TCP 快速打开（Passive TFO）机制会在 SYN 报文未携带数据时，仍然接受带有有效 Cookie 的 SYN 报文。在这种情况下，子套接字的接收队列会被有意保持为空。 函数在检查是否存在已入队的 SYN 数据之前，就设置了 标志。这导致没有携带数据的 TFO SYN 触发内核警告（WARN）；如果该警告并非致命错误，则会遗留过时

CVSS 9.4 · Critical EPSS 0.31% · P23

Possible ATT&CK Techniques 1 AI

T1201.001

Affected Version Matrix 12

VendorProduct Version RangeStatus
Linux Linux 36b122baf6a8bd46b4a591f12f4ed17b22257408< f75f174edc865738522e514d042cf5627f084859 affected
36b122baf6a8bd46b4a591f12f4ed17b22257408< fca7e444c04689fe4cc6b56f2725f804a4bb1ef9 affected
36b122baf6a8bd46b4a591f12f4ed17b22257408< 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5 affected
36b122baf6a8bd46b4a591f12f4ed17b22257408< 72b4a0c51a4b550d40301d60a366b429b8c8e78d affected
36b122baf6a8bd46b4a591f12f4ed17b22257408< e00b63056fb4f261455b3e5df5268a1f8ce47a87 affected
6.2 affected
< 6.2 unaffected
6.6.153≤ 6.6.* unaffected
… +4 more rows
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I. Basic Information for CVE-2026-80585

Vulnerability Information
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Vulnerability Title
mptcp: fastopen: only mark MPTFO subflows with SYN data
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: mptcp: fastopen: only mark MPTFO subflows with SYN data Passive TCP Fast Open accepts a valid-cookie SYN even when it carries no data. In that case the child socket's receive queue is intentionally left empty. mptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking for queued SYN data. That made data-less TFO SYNs hit a WARN and, if the warning was non-fatal, left stale MPTFO state behind. The stale flag could later trigger a state-confusion bug in check_fully_established(). Only mark the subflow as MPTFO after confirming that an SKB was queued. Return quietly when the receive queue is empty. Note that mptcp_subflow_context's is_mptfo field is now not just about subflows where the TFO was present, but about MPTFO subflow that consumed SYN data. Only having a valid cookie but not carrying data is not really "doing TFO".
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 36b122baf6a8bd46b4a591f12f4ed17b22257408 ~ f75f174edc865738522e514d042cf5627f084859 -
Linux Linux 6.2 -

II. Public POCs for CVE-2026-80585

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III. Intelligence Information for CVE-2026-80585

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Patches & Fixes for CVE-2026-80585 (5)

Same Patch Batch · Linux · 2026-08-26 · 92 CVEs total

CVE-2026-80589 9.8 CRITICAL block: stop the timeout timer when releasing a never added disk
CVE-2026-74752 9.8 CRITICAL sctp: validate cookie AUTH state before use
CVE-2026-80519 9.8 CRITICAL ovpn: finish crypto callback cleanup before peer release
CVE-2026-74746 9.8 CRITICAL netfilter: flowtable: publish GC-visible tuple last
CVE-2026-80528 9.8 CRITICAL ceph: avoid fs reclaim while using current->journal_info
CVE-2026-74744 9.8 CRITICAL ipvlan: inherit needed_headroom and needed_tailroom from phy_dev
CVE-2026-74743 9.8 CRITICAL macvlan: inherit needed_headroom and needed_tailroom from lowerdev
CVE-2026-80561 9.8 CRITICAL libceph: fix multiple unsafe decodes in decode_locker()
CVE-2026-80558 9.8 CRITICAL libceph: Avoid using invalid osd indices from primary_temp
CVE-2026-80586 9.8 CRITICAL mptcp: options: reset DSS fields in case of unexpected size
CVE-2026-80557 9.8 CRITICAL libceph: fix OOB read in decode_watchers() via missing bounds check
CVE-2026-74737 9.8 CRITICAL net: ethernet: ti: am65-cpsw-nuss: Fix port_id extraction from SRC TAG
CVE-2026-80587 9.8 CRITICAL mptcp: avoid combining some incoming suboptions
CVE-2026-74751 9.4 CRITICAL riscv: lib: Fix ZBB strnlen reading past count boundary
CVE-2026-80554 9.3 CRITICAL s390/vfio_ccw: Limit the number of channel program segments
CVE-2026-80551 9.3 CRITICAL s390/vfio_ccw: Ensure first IDAW remains constant
CVE-2026-80547 8.8 HIGH s390/vfio_ccw: Implement a crw lock
CVE-2026-80576 8.8 HIGH drm/amdgpu: reject oversized IBs with per-ring packet limits
CVE-2026-80552 8.8 HIGH s390/vfio_ccw: Ensure index for read/write regions are within range
CVE-2026-80553 8.8 HIGH s390/vfio_ccw: Cancel existing workqueues

Showing top 20 of 92 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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